Flow control

ABSTRACT

The present invention relates to a device for controlling the flow through an oil cooler, comprising at least one oil tank ( 1 ) and at least one oil pump ( 7 ), a means ( 12 ) for determining the oil temperature, a cooling means ( 4 ) for cooling the oil, wherein said means ( 4 ) can be circumvented via a bypass ( 9 ), as well as an engine control unit ( 13 ). The device has a means ( 11 ), controllable via the engine control unit ( 13 ) by which the oil flow can be controlled via the means for cooling ( 4 ) and/or via the bypass ( 9 ). The device further comprises a means for predictively controlling the oil flow via the cooling means ( 4 ) and/or via the bypass ( 9 ).

The invention relates to a device for controlling the flow of oilthrough an oil cooler. In particular the invention relates to such adevice for use on vehicles, such as agricultural machines.

Devices for controlling the flow of oil through an oil cooler are known.FIG. 1 by way of example shows a block diagram of working ortransmission hydraulics, as are usual in mobile machines. An oil tank 1holds a volume of oil. An oil-air cooler 4 is arranged in front of this.This cooler 4 has a bypass valve 5 connected in parallel. The actualcircuit of the vehicle can vary greatly depending upon the scope ofapplication and is simply represented by symbol 6. An oil pump 7 withconstant displacement is used for supplying the circuit 6. Other pumpswith constant or variable displacement can also be used in addition tothis pump. If only one pump is used, usually this works with constantdisplacement. In front of the cooler 4 a sensor 8 is provided fordetermining the dynamic pressure. The bypass valve 5 connected inparallel has a spring tension of 5 bar for example. The parallelconnection of the bypass valve 5 ensures that a maximum decrease inpressure of 5 bar can occur over the cooler 4. Consequently the cooler 4is protected from too high internal pressures, which could exceed thepermissible bursting pressure. Thus valve 5 represents a simple andreliable means of protection for the cooler 4.

A disadvantage of this arrangement is that even at low oil temperaturesoil always flows through the cooler 4. The constant, actually unwanted,cooling of the oil at low temperatures is a side effect of thisarrangement. It stems from the fact that oil warms up relatively slowly.Slow warming of the oil produces losses of efficiency and can alsoresult in malfunction of valves or cavitation in pumps. Thedisadvantages mentioned occur even if an oil-oil heat exchanger or anoil-water heat exchanger is used instead of the oil-air cooler 4. In anoil-oil heat exchanger, outside air is not used as cooling agent for thecooling medium but a second oil. This oil originates from another oilcircuit and, as cooling agent, has a lower temperature than the mediumto be cooled.

FIG. 2 shows an alternative embodiment to FIG. 1. In this case thebypass valve 5 has been replaced by a thermostatically-controlled oiltemperature regulator OETR 5. The OETR 5 has as many intermediatepositions as desired. In position a, the OETR 5 opens a bypass branch 9to the tank 1 and completely closes the inflow 10 to the cooler 4. Thisposition is assumed at low temperatures. An expanding material element17 which is provided on one side of the OETR 5 ensures that in the basicsetting the OETR 5 assumes a position, wherein the entire oil isdirected via the bypass branch 9, is provided on one side of the OETR 5.The expanding material element 17 expands when the oil temperaturerises. As a result of the expansion of the expanding material element 17against a spring 5 a the valve moves to operating position b, thusgradually releasing the oil flow to the cooler 4 and gradually closingthe flow to the bypass 9 for the cooler 4. In operating position b theoil flows both via the bypass branch 9 and via the cooler inflow 10.With increasing oil temperature the valve moves to operating position c,the oil now flowing completely to the cooler 4 in order to reach a highcooling capacity. The passage to the bypass branch 9 is blocked.

The disadvantage of this circuitry is that the OETR 5 represents acomparatively large and expensive component. The total amount of oilmust always flow through the OETR and the oil reacts relativelysluggishly to changes in temperature. Furthermore the switching responsecannot be influenced, for example to adapt to different operatingconditions. The disadvantages mentioned occur even if an oil-oil heatexchanger or an oil-water heat exchanger is used instead of the oil-aircooler 4.

On this basis it is an object of the present invention to avoid thedisadvantages of the aforementioned flow control devices in a simple andeconomical way. According to one aspect of the invention there isprovided a device for controlling the flow through an oil cooler,comprising at least one oil tank, at least one oil pump, an oiltemperature measurement means for determining the oil temperature, acooling means for cooling the oil and an engine control unit whereinsaid cooling means can be circumvented via a bypass and the device has aflow control means controllable by the engine control unit to controlthe oil flow through the cooling means and/or via the bypass,characterised in that the device has a predictive means for predictivelycontrolling the oil flow via the cooling means and/or via the bypass.

In this case predictive means the prognostic control of the oil flow.Such control prevents temperature spikes in the oil, which can developif a circuit reacts too slowly to a rise in temperature. Predictivecontrol for example can be implemented by data determined by atemperature sensor being passed onto an engine control unit andevaluated by this. The oil temperature in this case is used as a controlvariable of a characteristic diagram. Based on this the engine controlunit continually calculates a temperature gradient, that is to say thetemperature rise or temperature fall is continually monitored over time.If a high temperature gradient is detected, a higher cooling capacitydemand results in order to prevent the permissible limit temperature ofthe oil from being exceeded. By closing the means for controlling theoil flow, a larger quantity of oil is fed to the cooler and thus thecooling capacity is increased.

According to a further aspect of the invention there is provided amethod for controlling the oil temperature in a device, comprising thefollowing steps:

-   -   Determination of the oil temperature by oil temperature        measurement means transmission of the determined values to the        engine control unit,    -   computation of the cooling capacity demand,    -   control of the oil flow via the cooling means and/or via the        bypass, wherein the control takes place via the flow control        means, characterised in that the method is carried out        predictively.

The flow control device has a control means controllable via the enginecontrol unit for controlling the oil flow through the cooling meansand/or via the bypass.

Thus, a substantial improvement is obtained in relation to the priorart. The cooler is substantially better protected from damage. This isattributed to the fact that in operation the internal pressure is alwaysless than the bursting pressure. Furthermore warming of the oil issubstantially accelerated due to the fact that the bypass branch can bekept open for a long time. A further advantage is that the dynamicpressures before the cooler, which are usually known to be high can beavoided. This is important to the extent that the high dynamic pressurescan have disadvantageous functional effects on the operation of thehydraulic system.

In a preferred embodiment the flow control means controllable via theengine control unit is a proportional throttle valve and/or an on-offvalve and/or a hydraulic check valve.

It has also been proved advantageous to control the engine speed fromthe engine control unit, since the delivery of the pump is proportionalto the engine speed. In the event that the drive speed of the pump fallsand the oil temperature rises at the same time this form of control isparticularly advantageous. This operational case is to be found quitefrequently in working hydraulics since high energy loss and rising oiltemperatures occur at average engine speeds. In the case of fallingengine speeds and reduced output from the pump, the cooling capacity ofthe oil cooler reduces, although due to rising oil temperature a highercooling capacity demand is present. As a result of the preferredembodiment the possibility now exists of closing the means forcontrolling the oil flow further and of increasing the oil flow to thecooler despite falling engine speed. Thus the reduction in the oil flowthrough the cooler can be compensated by closing the bypass valve morepowerfully and thus achieving a higher cooling capacity. The advantagesmentioned occur even if an oil-oil heat exchanger or an oil-water heatexchanger is used in place of the oil-air cooler.

In a further advantageous embodiment of the invention the means forcooling the oil temperature is an oil-air cooler and/or an oil-oil heatexchanger and/or an oil-water heat exchanger.

Additionally it has proved advantageous if the flow control device has areflux filter. In this case it is of particular advantage if this refluxfilter can be freely circumvented via a bypass valve.

It has also proved particularly advantageous if the device, in apreferred embodiment, has two separate circuits for the working andtransmission hydraulics.

Of really special preference in this case is a vehicle, in particular atractor, which comprises a device in accordance with the abovedescription.

The invention will now be described, by way of example only, withreference to the following drawings in which:

FIG. 1 is a flow control device in the prior art;

FIG. 2 is another flow control device in the prior art;

FIG. 3 is a preferred embodiment of the invention;

FIG. 4 is a further preferred embodiment, in which the controllablemeans is an on-off valve;

FIG. 5 is a further embodiment, in which a hydraulic check valve isused;

FIG. 6 is a further embodiment of the invention, in which the circuitsfor the working and transmission hydraulics are separate;

FIG. 7 is a further preferred embodiment; and

FIG. 8 is an embodiment, in which the circuit has been simplified.

In the following explanations the reference symbols designate the sameor comparable parts.

FIG. 3 shows a preferred embodiment of a flow control device throughwhich oil from an oil tank 1 flows. The device has a flow control means11, with as many intermediate positions as desired, for controlling theoil flow. A temperature sensor 12, which is present in the system,continuously measures the oil temperature in the inflow 10 of the cooler4 and transmits this to an engine control unit (ECU) 13. The enginecontrol unit 13 has an output, which can be a pulse-width-modulation(PWM) output which activates an oil flow control means 11. If the oil iscold there is no activation of the oil flow control means; thus thebypass branch 9 is completely open in operating position a. Thecomponent cooler 4 comprising the valve and the pipes is designed suchthat none or only very little oil flows over the cooler 4. When the oiltemperature increases the oil flow control means 11 is activated, tooperating position b directing a portion of the oil flow, dependent uponthe level of increase in the oil temperature, to the cooler inflow 10and the remaining portion to the bypass branch 9. With higher oiltemperatures and demands for higher cooling capacity the oil flowcontrol means 11 is completely closed, to operating position c, and theentire oil flow is directed to the cooler 4. A characteristic diagramwhich is based on measurements or calculations can be programmed in theengine control unit 13.

Here the following applies:

Q _(ges) =Q _(BP) +Q _(K)

Q _(BP) =f(I)

Q _(ges) =f(n)

Q _(K) =Q _(ges) −Q _(BP)

wherein:Ges=entire,BP=bypass,K=cooler,I=current andn=engine speed.

From this it can be derived what current (I) is necessary, in order fora given oil temperature and engine speed (n) to direct a certain oilflow to the cooler, so as to obtain a certain cooling capacity. In theevent of power failure or cable break the oil flow control means 11changes to the bypass position a and therefore it is guaranteed that thebypass 9 is opened, and in cold weather starting conditions the cooler 4suffers no damage. In the event of an error, for example, a cable breakor short-circuit in the electrical connection between engine controlunit 13 and oil flow control means 11, the operator can close the oilflow control means 11 by switching an emergency manual control d andthus ensure cooling.

FIG. 4 shows a further preferred embodiment of the flow control device.In this embodiment a 2/2 on-off valve is used as oil flow control means11. Instead of having as many intermediate positions as desired only thetwo fixed operating positions c and a are provided. The advantagesspecified in FIG. 3 are also valid for FIG. 4 with the difference thaton and off switching of the cooler 4 takes place without intermediatesteps.

FIG. 5 shows a further preferred embodiment of the flow control device.This preferred embodiment, as the oil flow control means 11, has anelectrically-operated check valve 11. This check valve by way of examplehas a response pressure of 5 bar. The check valve 11 is opened by anelectric current, directing the oil flow to the bypass 9 and ensuringthat the cooling capacity is reduced, in order to guarantee fast oilwarming. In the event of power failure or a cable break, the check valve11 changes to the bypass position a and therefore ensures that thebypass 9 is opened and the cooler 4 does not suffer damage in coldweather starting conditions. As an advantage of this embodiment it ismentioned that the fail safe function of the means 11, fulfils both therequirement to limit the cooler internal pressure and providing thecooling capacity, without making additional emergency hand operationnecessary.

FIG. 6 shows a preferred embodiment, in which the circuit for theworking and transmission hydraulics are separate. An oil pump 7 a withconstant displacement draws from a tank 1 a and feeds the workinghydraulics circuit 6 a. The working hydraulics circuit 6 a can also besupplied by further pumps not illustrated here. In this case onlyfurther circuitry of the working hydraulics circuit 6 a is fed by thepump 7 a. The flow control means 11 a which is connected in parallel toa heat exchanger 14 is located in the further circuitry. An oil pump 7 bwith constant displacement draws from a tank 1 b and feeds the hydraulicsystem 6 b. The transmission hydraulic system 6 b can also be suppliedby further pumps, not illustrated here. Of significance here is that thefurther circuitry of the transmission hydraulics 6 b is only fed by pump7 b. A cooling means 4 which is protected by the parallel-connectedmeans 11 c is located in the further circuitry. The second side of theheat exchanger 14 is located in the further circuitry of the cooler 4.The heat exchanger 14 can be of a plate or of a tube bundleconstruction. The heat exchanger 14 is designed to transfer the heatenergy of the oil circuit at the higher temperature to the circuit atthe lower temperature. The temperatures of the transmission oil circuit6 b are measured by the temperature sensors 12 b and 12 c, thetemperature of the working hydraulic system 6 a being measured by thetemperature sensor 12 a. The sensors 12 a, 12 b and 12 c are connectedto the engine control unit 13, so that the flow control means 11 a, 11 band 11 c are activated. Thus each of the individual coolers has anelement to control the temperature and to control the cooling capacity.The advantages of the cooler control therefore have an effect in each ofthe individual circuits.

If a vehicle is started in the cold and while standing or during slowjourneys delivers high hydraulic power, this can lead to the fact thatthe oil temperature in the working hydraulic system 6 a rises veryquickly and the oil temperature in the transmission oil circuit 6 bremains low. For certain groups of vehicles such as agriculturaltractors this is a typical case of operation. The flow control means 11a in the working hydraulic system would be fully activated and closed,since a high temperature is registered in the working hydraulic system 6a and a high cooling capacity should be obtained. The flow control means11 b and 11 c are now not activated and open, since a low temperature isregistered in the transmission oil circuit 6 b and the oil is directedto the cooling means 4 and to the heat exchanger 14. Since no coolingagent flows through the heat exchanger 14, the oil in the workinghydraulic system 6 a is not cooled and there is a danger of overheating.This problem is solved by the preferred embodiment in the following way:above a certain temperature difference between temperature sensors 12 aand 12 b, the flow control means 11 b is closed by energisation and thecooling agent is directed to the heat exchanger 14. As a result thetemperature in the circuit 6 a falls and the temperature in the circuit6 b rises. This heat transfer has the consequence that circuit 6 a isprotected from overheating and the circuit 6 b is warmed up. The heatingof the oil in circuit 6 b improves the efficiency in circuit 6 b. Thusfuel consumption is reduced, whenever the vehicle starts to move afterstationary operation. If the temperature at sensor 12 c rises above acertain level, it is necessary to dissipate heat energy from the vehicleinto the environment. This takes place by energizing the flow controlmeans 11 c. By specific activation of the flow control means 11 c thecooling capacity of the cooling means can be regulated within certainlimits. In the event that the transmission oil becomes hot due to fastroad travel, the flow control means 11 c and 11 b are opened. The oil incircuit 6 a remains at a low temperature for a long time if the workinghydraulics 6 a are not running, as is usual in the case of road travel.This is particularly the case if circuit 6 a is equipped with one ormore variable pumps (not illustrated). Due to the low-loss standbyoperation of this type of pump the oil only warms up very slowly. Thepreferred embodiment solves this problem as follows: above a certaintemperature difference between temperature sensors 12 b and 12 a, theflow control means 11 a is activated and closed, and the medium to bewarmed up in circuit 6 a is directed to the heat exchanger 14. Thus thetemperature in the circuit 6 a rises and the temperature in the circuit6 b falls. This heat transfer has the consequence that the temperaturein the circuit 6 b reduces and the oil in circuit 6 a warms up. Theheating of the oil in circuit 6 a reduces the likelihood of cavitiesforming in the pumps in circuit 6 a. Furthermore as a result of theheating of the oil, the switching times of the solenoid valves incircuit 6 a are reduced, and their operational reliability improved. Bythis method of controlled heat transfer the circuit—not illustrated indetail—under certain circumstances may be simplified, while other meansfor heating the oil can be dispensed with.

FIG. 7 shows a further preferred embodiment of the invention. The flowcontrol means 11 c has been replaced by the check valve 16. The checkvalve 16 takes over the function of protecting the cooler 4 from toohigh internal pressure and indirectly takes over the flow control andthus the cooling performance.

FIG. 8 shows a further preferred embodiment of the invention. The flowcontrol means 11 b and 11 c from FIG. 6 or 11 b and the check valve 16from FIG. 7 are replaced by a single control means 11 b, in order toreduce the component complexity and the costs. In the circuit accordingto FIG. 8, heat energy can be transferred in a controlled way fromcircuit 6 a to 6 b and from circuit 6 b to circuit 6 a. The circuitaccording to FIG. 8 does not offer the possibility of separating thecontrol for the performance of cooler 4 from the control for theperformance of heat exchanger 14.

1-9. (canceled)
 10. An oil cooling arrangement comprising: a first transmission oil cooling circuit including a first oil pump, a first oil tank, a first oil temperature sensing means and an oil cooler; a second separate oil cooling circuit for hydraulic consumers including a second oil pump, a second oil tank and a second oil temperature sensing means; the two circuits being thermally interconnected by a heater exchanger through which both circuits flow separately; by pass means in the first circuit for bypassing flow in the first circuit around the cooler and heat exchanger; by pass means in the second circuit for bypassing flow in the second circuit around the heat exchanger, and control means arranged to receive signals from the first and second temperature sensing means and for opening at least one of the bypass means in a predictable manner dependent on the temperature signals received by the control means.
 11. An arrangement according to claim 10 in which the cooler and heat exchanger in the first circuit each have their own bypass means which is controlled by the control means and the heat exchanger has its own bypass means in the second circuit also controlled by the control means.
 12. An arrangement according to claim 11 in which the bypass means each comprise solenoid operated fluid flow control valves connected in parallel to the cooler and heat exchanger in the first and second circuits.
 13. An arrangement according to claim 10 in which the cooler and heat exchanger each have their own by-pass means in the first and second circuits, the bypass means for the heat exchanger in the first and second circuits comprising solenoid operated fluid flow control valves operated by the control means, and the by pass means for the cooler comprises a spring loaded check valve.
 14. An arrangement according to claim 10 in which the cooler and heat exchanger have a single by pass means which by passes both the cooler and heat exchanger and which is operated by the control means.
 15. An arrangement according to claim 10 in which the single by pass means comprises a single solenoid operated fluid flow control valve controlled by the control means.
 16. An arrangement according to claim 14 in which the by pass means for the heat exchanger in the second circuit comprises a solenoid operated fluid flow control valve controlled by the control means. 